Outlook and Zimbra calendar without MAPI

Ok so how does this work? How does the Zimbra web client's calendar talk to the Zimbra server? Through some kind of iCal protocol or something? Whatever method that is, could I get Outlook to speak that protocol too? I don't want to pay for (or wait for) the MAPI connector, but couldn't I find a way to get Outlook talking whatever protocol the Zimbra server uses to talk to its own web client or whatever other protocols it already supports for calendaring?

Imap/pop

Speaking soap....

Ok well if you speak soap, are you speaking some well-standardized soap language to talk back and forth between a calendar and a server, or is it a set of commands you guys came up with? In other words, is it "possible" (from a theoretical standpoint, I'm not asking if you know if such a thing exists) that I could find some plugin to Outlook (or any other calendaring program) that would talk to your soap calendar? Or did you guys use soap as an open API yet came up with your own command set using that API to talk back and forth between the calendaring program and the server, which I imagine would mean that any plugin to Outlook or anything else to make its calendar talk to Zimbra would have to have been specifically developed to talk to Zimbra, not just some standardized "soap calendaring protocol" or something?